The present invention relates to a control device for textile machines, in particular for crochet machines.
It is known that crochet machines comprise a needle bar bearing a plurality of needles, a guide bar bearing a plurality of eye-pointed needles and at least one carrier slide bar bearing a predetermined number of threading tubes. These bars cooperate with each other carrying out synchronized movements for manufacturing fabrics and textile products in general.
To move the different members composing said crochet machines and in particular the carrier slide bars, some of the most advanced crochet machines are equipped with suitably-operated electric motors with which rotary encoders are generally associated; each encoder has the task of detecting the angular position of the output shaft of a corresponding motor and communicate this data to the machine control system, so as to enable correct regulation of the movement of the different members through the respective motors.
Generally, each motor is capable of moving the respective member by making its output shaft carry out rotations of less than 360°; in other words, through rotations that do not reach a full revolution, each output shaft succeeds in moving the knitting member interlocked therewith to all the required positions.
In order to improve movement accuracy and reliability of the different members, reduction gears have been inserted between the output shaft of the motor and the corresponding knitting member; therefore, to bring the knitting member from an extremity to the other of its stroke, the shaft of each motor must carry out several revolutions.
However, some operating drawbacks are connected with the manufacturing choice briefly described above.
In fact, the encoder associated with each motor is a simple absolute single-revolution encoder, i.e. capable of only detecting the angular position of the output shaft, without recognizing to which revolution such a position corresponds; in other words, by said encoders currently mounted on the motors present in crochet machines, it is possible to known the angular position of the shaft with reference to a single revolution (i.e. a value included between 0° and 360°), even if the true movement of the shaft can be performed in several revolutions (in the case of five revolutions, there is an overall value of possible 1800° rotation) for a single movement of the member associated therewith.
Therefore, when at the moment of turning the machine off the weft bars are required to be manually shifted (for carrying out maintenance or cleaning operations, for example), the information concerning the true position of these bars—i.e. the absolute position of the output shaft of the corresponding motor—is lost, because the only available detecting instrument is said single-revolution encoder that is not able to supply a correct information relating to displacements of some importance (corresponding to rotations exceeding 360° of the output shaft of the corresponding motor) occurred during the machine deactivation.
Consequently, upon restarting of the machine, when the weft bars are moved in accordance with the program inputted to the respective drive means, serious damages may occur both to possible semifinished products in engagement with the machine members and to the devices of the machine itself; in fact, since the drive means is not acquainted with the exact position of the members to be moved, it can impose movements to the bars that are beyond the end positions allowed to them or movements submitting the weft yarns to too strong tensions causing breaking of the yarns.
To remedy this drawback, the known art has only supplied solutions preventing the machine members, and in particular the weft bars, from moving when the machine is turned off; these solutions typically involve mechanical, magnetic or electromagnetic brakes that are active on the bars, or kinematic connecting mechanisms of the screw-nut screw type.
It is however apparent that technical solutions as those described above prevent a regular execution of the maintenance and cleaning operations on the machine, and therefore they do not meet the operators' requirements in the concerned technical field.